Method of Bonding Two Substrates and Device Manufactured Thereby

ABSTRACT

The invention relates to method for bonding at least two substrates, for example made from glass, silicon, ceramic, aluminum, or boron, by using an intermediate thin film metal layer for providing the bonding, said method comprising the following steps of: a) providing said two substrates; b) depositing said thin film metal layer on at least a part of a surface of a first substrate of the two substrates; c) bringing a surface of the second substrate into contact with said thin film metal layer on said surface of the first substrate such that a bonding between the second substrate and the thin film metal layer on the first substrate is provided; and d) at least locally strengthening the bonding between the second substrate and the thin film metal layer on the first substrate. The invention also relates to a device comprising two substrates, for example made from glass, silicon, ceramic, aluminum, or boron, and an intermediate thin film metal layer.

The invention relates to a method for bonding at least two substrates,for example made from glass, silicon, ceramic, aluminum, or boron.

Known methods for bonding at least two substrates, for example made fromglass, silicon or ceramic, make use of heating the two substrates afterthey are brought into contact with each other. However, for certainapplications heating of the two substrates in order to provide thebonding is undesirable. For example, substrates provided with anorganic-based anti-stiction coating and/or immobilized molecules aretemperature sensitive and cannot be heated.

It is therefore an object of the invention to provide a method forbonding two substrates, for example made from glass, silicon or ceramic,that allows for other means for bonding than heating.

This objective is achieved by a method according to the preamble and byusing an intermediate thin film metal layer for providing the bonding,said method comprising the following steps of:

a) providing said two substrates; b) depositing said thin film metallayer on at least a part of a surface of a first substrate of the twosubstrates;

c) bringing a surface of the second substrate into contact with saidthin film metal layer on said surface of the first substrate such that abonding between the second substrate and the thin film metal layer onthe first substrate is provided; and d) at least locally strengtheningthe bonding between the second substrate and the thin film metal layeron the first substrate.

Providing a thin film metal layer between the two substrates has theadvantage that this allows the bonding between the two substrates andthe thin film metal layer to be strengthened by various means. Suchvarious means will be described below with respect to differentembodiments of the method according to the invention.

The thin film metal layer may have a maximum thickness of about 500 nm,preferable a maximum thickness of about 250 nm, even more preferableapproximately 40 nm. It is found that with such a thin film metal layera good initial bonding between the thin film metal layer and the secondsubstrate is provided after step (c). Such an initial bonding allows foran easy handling of the device produced by the method according to theinvention, which device comprises the two substrates and theintermediate thin film metal layer, even before the bonding isstrengthened in step (d). The device produced by the method accordingthe invention may be a so called microelectromechanical system (MEMS)device or a microfluidic device or chip.

A plurality of substrates may be bonded by means of the method accordingto the invention.

Each substrate may comprise glass, silicon, ceramic, or a combinationthereof. For example, two glass substrates may be bonded to each otherby the method according to the invention, such that a glass-metal-glassdevice is obtained. The two glass substrates may comprise borosilicate,soda lime, sapphire or quartz. Alternatively, such a glass substrate maybe bonded to a silicon substrate, such that a glass-metal-silicon deviceis obtained.

In order to provide a good bonding between the two substrates and thethin film metal layer, the first substrate and/or the second substrateis preferably cleaned, at least previous to step (b) and/or respectivelystep (c). Such surface cleaning is known per se and suitableconventional cleaning means may be used.

In an embodiment of the method according to the invention said thin filmmetal layer comprises a metal chosen from the group comprisingpalladium, copper, tungsten, aluminum, cobalt, nickel, thalium,ruthenium, iron, molybdenum, stainless steel, chromium, tantalum,vanadium, and titanium, and wherein said thin film metal layer comprisesa metal oxide layer.

The applicant has found that as a result of the metal oxide layer abonding between the two substrates and the thin film metal layercomprising the metal oxide layer is provided. In particular, the metalschosen from this group and comprising said oxide layer promote bondingby chemical interaction of the metal oxide with the substrate formingoxo bridges, as for example, M—O—S— bonds at the surface of thesubstrates. Here, substrate S is for example silicon (Si), aluminum(Al), Boron (B), glass or ceramic. Metal M is for example palladium(Pd), copper (Cu), tungsten (W), aluminum (Al), cobalt (Co), nickel(Ni), thalium (Ti), ruthenium (Ru), iron (Fe), molybdenum (Mo),stainless steel, chromium (Cr), tantalum (Ta), vanadium (V), or titanium(Ti). In each case, the metal is capable of existing in one of severalstable oxidation states, ranging from 2+ in case of Ni (NiO) to 5+ incase of Ta (Ta₂O₅), and it is preferably a transition metal or alanthanide. Most preferred are metals such as Cr (forming CrO, Cr₂O₃,Cr₂ O₅) which can form stable oxo bridged anions such as chromates andperchromates. The thickness of the metal oxide layer may be chosen inaccordance with the required bonding strength. The thin film metal layermay be integrally formed with the metal oxide layer or the metal oxidelayer may a layer on the thin film metal layer. The applicant has foundthat particularly chromium and tantalum are suitable for bonding the twosubstrates.

In an alternative embodiment of the method according to the inventionsaid thin film metal layer comprises a metal chosen from the groupcomprising silver, platinum and gold.

Such metals do not form metal oxide and are soft, so deformable,enabling the formation of an extended molecular contact that covers theentire bonding area without any microscopic air gaps or gaps undervacuum in which the application of an energy source leads to a localmelting of the metal allowing diffusion of liquid or softened metal intothe microscopic crevices of the substrates, hence increase the area ofcontact and hence form a bond. For example such metals are noble metals.The applicant has found that in particular gold is well suitable forbonding the two substrates.

It has also been found that combinations of metals from the abovedescribed two groups work well, for example, an alloy of Gold andTantalum is especially preferred in which gold softens and wets thebonding surfaces, while Tantalum forms oxo bridged structures across theinterface.

In an embodiment of the method according to the invention step d) isperformed by urging the two substrates together.

Due to such a mechanical pressure the thin film metal layer may deform,such that the bond between the two substrates and the intermediate thinfilm metal layer is strengthened. The applicant has found thatstrengthening the bond by means of mechanical pressure is especiallysuitable if use is made of a relatively soft thin film metal layer, suchas gold.

Alternatively or additionally step (d) is performed by at least locallyheating said thin film metal layer. By means of at least locally heatingsaid thin film metal layer at least a local substrate-metal-substratejoint is generated, such that the bonding between the two substrates andthe thin film metal layer is at least locally strengthened.

Such (locally) heating of the thin film metal layer may be performed bymeans of a laser wherein at least one of the substrates is transparentfor said laser, an electric current, microwave radiation or ultrasonicenergy.

Heating said thin film metal layer by means of a laser has the advantagethat the thin film metal layer absorbs the laser radiation, because atleast one of the two substrates is transparent for said laser, such thatthe temperature of the two substrates is not, or only slightly,increased. Due to that the temperature of the two substrates is not, oronly slightly, increased, this method is suitable for temperaturesensitive devices, for example said devices provided with anorganic-based anti-stiction coating and/or immobilized molecules.Temperature sensitive devices are defined here as devices that cannot beheated to a temperature of 100° C. or more without damage. Said laser ispreferably a pico-, femto-, or attoseconds laser which generates shorthigh power pulses. In particular laser pulses in green or near infraredand of pulse width in the range of 0.1-20 picoseconds is preferred,since such a laser pulse has a high peak power, in the range of 10-1000MW, while delivering a small energy per pulse, preferably in the rangeof 10-1000 micro joules. Longer laser pulses (e.g., those of duration1-20 nanoseconds) deliver more energy per pulse and a lower peak power,while shorter laser pulses (less than 0.1 picoseconds) deliver too lowan amount of energy per pulse (less than 10 micro joules per pulsewithout amplification) and increase processing time. This combination ofpeak power and energy per pulse promotes photoinonization and ultrarapid(supersonic) transfer of energy via ballistic electrons that are formedby photoionization of the metal coating, while the extent of heattransfer through a diffusion wave (sonic or subsonic) remains relativelyunimportant (less than 10% of the total energy delivered). This mode ofenergy transfer keeps the temperature rise (defined as a rise intemperature of 10° C. or more) confined to within 1-10 microns, leadingto the maximum utilization of applied energy to bond formation ratherthan dissipation by heating the substrates. In particular such acombination of peak power and energy per pulse offers optimization ofthe laser bonding process that minimizes: laser induced damage(including ablation), diffusive dispersion of laser energy in the formof heat, causing temperature rise in areas adjacent to the bond line,and processing time. Such a bonding process is preferred for fabricationof hermetically sealed packages for use in implants, or bond linessituated less than 1 mm from temperature sensitive MEMs or microfluidiccomponents.

As a result of that the thin film metal layer is, at least partially,electrically conductive, an electric current may be applied to the thinfilm metal layer. As a result of resistive heating the thin film metallayer is heated and the bonding between the thin film metal layer andthe two substrates is strengthened. Due to that only the thin film metallayer is heated, the temperature of the two substrates is not, or onlyslightly, increased, such that this method is also suitable fortemperature sensitive devices.

By means of microwave radiation the thin film metal layer is heated dueto dielectric heating. Due to that only the thin film metal layer isheated, the temperature of the two substrates is not, or only slightly,increased, such that this method is also suitable for temperaturesensitive devices.

Alternatively, ultrasonic energy may be used to heat the thin film metallayer.

Alternatively or additionally step (d) is performed by heating the twosubstrates and the intermediate thin film metal layer in an oven. Theoven may be set to any desired temperature. Due to the presence of theintermediate thin film metal layer according to the invention, lowertemperatures may be required in order to have a bonding between theintermediate thin film metal layer and the two substrates, such that theoven may be set to a temperature 200° C. or lower.

In addition to said heating by means of an oven, mechanical pressure forpressing the two substrates together as described above may be applied.Such a combination of heating and mechanical pressure for strengtheningthe bond between the thin film metal layer and the two substrates hasfound to be especially suitable if a relatively soft metal, for examplecopper or gold, is used.

Alternatively or additionally step (d) is performed by applying anunderpressure, for example a vacuum, to the two substrates and theintermediate thin film metal layer. Any water present between the twosubstrates and the intermediate thin film metal layer is therebyremoved, such that the bond is strengthened. An underpressure is definedas a pressure below atmospheric pressure.

In another embodiment of the method according to the invention:

at least one of the two substrates provided in step (a) comprises acavity;

step (b) is performed such that said thin film metal layer surrounds aportion of the surface of the first substrate;

step (c) is performed such that after step (c), said portion, saidcavity, and the inner surface of the thin film metal layer directed tosaid portion, define an inner space between said two substrates, and

step (d) is performed such that a sealing of the inner space betweensaid two substrates is provided.

The cavity may be a blind hole or a through hole in the substrate. Inone embodiment of the method the portion may comprise the cavity, suchthat step (b) is performed such that said thin film metal layersurrounds the cavity in the surface of the first substrate.Alternatively, the cavity may be included in the other substrate. Inthat case the two substrates are brought into contact with each other insuch a manner that the portion and the cavity mate.

The sealing may be hermetic, watertight, or dust tight, depending on theapplication of the device. A hermetic sealing is defined here as heliumleak tight according to predetermined standards. Due to such a sealingelectrical and/or mechanical and/or chemical and/or optical componentsand/or microfluidic structures present in the inner space between thetwo substrates are hermetic, watertight, or dust tight sealed from theoutside environment, thus making the device comprising said twosubstrates and the intermediate thin film metal layer suitable to beused as a MEMS device or a microfluidic device. A hermetically sealeddevice is especially suitable as an implantable device.

In yet another embodiment of the method according to the invention step(b) is performed such that it allows at least a part of said thin filmmetal layer to be used as an electrical connection and/or an opticalelement and/or a chemical element.

An advantage of having step (b) performed such that it allows at least apart of said thin film metal layer to be used as an electricalconnection and/or an optical element and/or a chemical element is thatsaid thin film metal layer may be used for bonding the two substrates aswell as for providing integrated electrical and/or optical and/orchemical structures, such that the resulting device is suitable to beused as a MEMS device. Such chemical components may comprise a catalyticlayer, a sensor or a reactive layer. Such optical components maycomprise a light blocking layer, a filter and a sensor. Said part of thethin film metal layer is preferably arranged at least partly within theinner space between the two substrates. The thin film metal layer may bedeposited on the first substrate by using standard lithographicaltechniques. Optionally, said part is not heated during any heating step.

Optionally step (b) is performed such that said part of said thin filmmetal layer that forms the electrical connection extends from the insideof the inner space to the outside of the inner space.

In even another embodiment of the method according to the invention saidheating is performed by irradiating a predetermined pattern in the thinfilm metal layer by means of a laser, wherein at least one of thesubstrates is transparent for said laser, and wherein said patterndefines an unirradiated second pattern that is electrically conductive.

By heating a predetermined pattern of the thin film metal layer by meansof a laser a substrate-metal-substrate joint is formed according to saidpattern. If said laser has suitable power, for example higher than 100mW, said laser creates a non-conductive pattern in the thin film metallayer. This is a result of that the irradiated parts of the thin filmmetal layer diffuse into the surrounding parts of the substrates. Thepart of the thin film metal layer that is not irradiated, which part isa second pattern defined by the predetermined irradiated pattern,remains electrically conductive. This embodiment of the method accordingto the invention thus has the advantage that simultaneously a bondingbetween the two substrates and the intermediate thin film metal layer isformed as well as an electrically conductive pattern.

Said irradiated pattern that is non-conductive may also be used forbreaking electrical circuits of the otherwise conductive metal layer.For example, if said metal layer surrounds an inner space, in whichinner space a component may be located, an irradiated pattern may beformed by said laser that crosses through the surrounding metal layer,such that no electric circuit is formed around said inner space. Such anembodiment is especially advantageous if said component is any componentsensitive to interference from a closed conduction circuit, for examplea magnetic sensor or a wireless communication device.

In an embodiment of the method according to the invention saidunirradiated second pattern extends from the inside of an inner space orthe inner space to the outside of the inner space.

This embodiment offers the advantage that the laser welds becomeelectrically non-conductive in order to define electrical connectionsbetween the inside and outside of the inner space.

Preferably, said thin film metal layer is biocompatible, whichbiocompatible layer comprises tantalum, gold and titanium, such that theresulting device may be used in implantable electrical, mechanicaland/or optical devices.

In a further embodiment of the method according to the invention saidmethod comprises the steps, to be performed after step (b) and beforestep (c), of:

e) depositing a resist on said thin film metal layer;

f) patterning said resist and said thin film metal layer on said part ofthe surface of the first substrate;

g) etching said first substrate comprising said thin film metal layerand said resist such that at least one microstructure is formed in saidfirst substrate; and

h) removing said resist such that said thin film metal layer remains onsaid first substrate.

An advantage of steps (e) to (h) is that the thin film metal layer maybe used as a mask layer as conventionally used in micromachining, suchthat the at least one microstructure may easily be formed in said firstsubstrate by using conventional etching techniques. Conventional etchingtechniques and etching means, suitable for etching of glass and/orsilicon and/or ceramics may be used.

After step (g) it is possible that some parts of the thin film metallayer overlap the microstructures. Due to that they overlap, a surfaceof the overlapping parts that is directed away from the resist is notcovered by the resist and/or the first substrate, such that surface ofthe overlapping part may be exposed to etching in order to adapt thewidth of the thin film metal layer to the width of the microstructure.In accordance herewith, said method preferably comprises the followingstep, to be performed after step (g) and before step (h), of;

i) etching parts of said thin film metal layer that overlap saidmicrostructure to compensate for underetching.

Any conventional etching techniques and etching means, suitable foretching of said metal may be used.

In a further embodiment of the method, according to claim 13 asdependent on 9, the sealing of the inner space between said twosubstrates is hermetic, and said method comprises the step of:

j) arranging temperature-sensitive components in the inner space.

The hermetic sealing allows for the arrangement of non-biocompatible,temperature sensitive components, such as liquid crystals or CMOS chips,in the inner space of an implantable device, by fully containing saidcomponents inside said device.

The invention also relates to a device, comprising two substrates, forexample made from glass, silicon, ceramic, aluminum, or boron, and anintermediate thin film metal layer, which device comprises an innerspace between the two substrates, which inner space is surrounded bysaid intermediate thin film metal layer that hermetically seals theinner space, wherein the thin film metal layer is biocompatible, andwherein temperature-sensitive components are arranged in said innerspace.

Such a device has the advantage that the hermetic sealing allows for thearrangement of non-biocompatible, temperature sensitive components, suchas liquid crystals or CMOS chips, in the inner space of an implantabledevice, by fully containing said components inside said device.

The invention further relates to the use of a thin film metal layer forbonding two substrates, for example made from glass, silicon, ceramic,aluminum, or boron, and for providing an electrical connection and/or anoptical component and/or a catalytic component.

The invention will now be explained in more detail with reference tofigures illustrated in a drawing, wherein:

FIGS. 1A-1C show the steps of a first embodiment of the method accordingto the invention;

FIG. 2 shows a device produced by a second embodiment of the methodaccording to the invention;

FIGS. 3A-3E show the steps of a third embodiment of the method accordingto the invention;

FIGS. 4A and 4B show two additional steps of the method of FIGS. 3A-3E;

FIG. 5 shows a second embodiment of a device produced by a fourthembodiment of the method according to the invention; and

FIG. 6 shows a third embodiment of a device produced by a fifthembodiment of the method according to the invention.

FIG. 7 shows a fourth embodiment of a device produced by a sixthembodiment of the method according to the invention.

FIGS. 1A-1C show the steps of a method for bonding two substrates, forexample made from glass, silicon or ceramic, using an intermediate thinfilm metal layer.

FIG. 1A shows the first step of the method, wherein a first substrate 1is provided. In this first step, a surface 2 of the substrate 1 iscleaned by means of conventional suitable cleaning means. Said surface 2is the lower main surface of the two main surfaces extending in thelongitudinal direction of said substrate 1.

Next, in the second step, a thin film metal layer 3 is deposited on thecleaned surface 2 of said substrate 1, as is shown in FIG. 1B. Due tothat said surface 2 is cleaned, the thin film metal layer 3 adheres wellto that surface 2.

In the third step, see FIG. 1C, the thin film metal layer 3 on thesurface 2 of the first substrate 1 is brought into contact with asurface 5 of a second substrate 4, such that a bonding between thesecond substrate 4 and the thin film metal layer 3 on the firstsubstrate 1 is provided. In order to have a relatively strong initialbonding the surface 5 is cleaned by means of conventional suitablecleaning means. Said surface 5 is the upper main surface of the two mainsurfaces extending in the longitudinal direction of said substrate 4.

After step three a device 6 is formed, comprising the two substrates 1,4 and the intermediate thin film metal layer 3, and with an initialbonding that is strong enough for allowing for an easy handling of thedevice 6. However, in order to use the device 6, for example as a MEMSdevice, the initial bonding between the thin film metal layer 3 and thetwo substrates 1, 4 needs to be strengthened in a fourth step. Due tothe thin film metal layer 3 according to the invention, various ways ofstrengthening the bond are possible, as is described above.

Optionally the device 6 may be cut into a plurality of parts, whereineach part is a device according to the invention. Production costs aresignificantly reduced if a relatively large device comprising twosubstrates and the intermediate thin film metal layer is formed and thencut into a plurality of devices.

It is noted that said thin film metal layer 3 may be deposited onanother surface of the first substrate 1, and that another surface ofthe second substrate 4 may be brought into contact with the surface ofthe first substrate 1 on which said thin film metal layer 3 isdeposited.

FIG. 2 shows a device 16 produced by a second embodiment of the methodaccording to the invention. The second embodiment of the method differsfrom the embodiment shown in FIGS. 1A-1C in that, in the second step, athin film metal layer 13 is deposited on a cleaned surface 12 of a firstsubstrate 11 according to a predetermined pattern. The cleaned surface12 is in this embodiment the upper main surface of the two main surfacesextending in the longitudinal direction of said substrate 11.

The predetermined pattern comprises an outer thin film metal layer 13A,which outer layer 13A surrounds a portion of the surface 12 of the firstsubstrate 11, such that after the second substrate 14 is brought intocontact with the first substrate 11, said portion defines a part of aninner space 18 between said two substrates 11, 14. The second substrate14 comprises a cavity or recess 19, such that said inner space 18 isdefined by said recess 19, the portion of said first substrate 11, andthe inner surface of the thin film metal layer directed to said portion.After strengthening the bond between said outer thin film metal layer13A and the two substrates 11, 14 in the fourth step, a hermetic sealingof the inner space 18 between said two substrates 11, 14 is provided.

The predetermined pattern further comprises an inner thin film metallayer 13B, which inner layer 13B is located near the center of the firstsubstrate 11. The inner layer 13B is used as an electrical connectionbetween components 17. If heating is used as the method step forstrengthening the bond between the intermediate thin film metal layer,said inner thin film metal layer 13B is optionally not heated.

A device 16 comprising said two substrates 11, 14, an intermediate thinfilm metal layer 13 and a hermetically sealed inner space 18 betweensaid two substrates 11, 14 is thus produced. In the inner space 18electrical and/or mechanical and/or chemical and/or optical componentsand/or microfluidic structures may be arranged, such that suchcomponents or structures are hermetically sealed from the outsideenvironment.

FIGS. 3A-3E shows the steps of a third embodiment of the methodaccording to the invention.

In FIG. 3A a first substrate 21 is provided. On a surface 22 of thefirst substrate 21 is a thin film metal layer 23 and a resist 30deposited.

In a next step the resist 30 and said thin film metal layer 23 on thesurface 22 of the first substrate 21 are patterned, see FIG. 3B, suchthat parts of the first substrate 21 to be etched are exposed.

In FIG. 3C said first substrate 21 comprising said thin film metal layer23 and said resist 30 are etched such that two microstructures 20 isformed in said first substrate 21. Said etching is performed by means ofconventional etching techniques and etching means, for example by meansof hydrofluoric acid (HF) etching.

In FIG. 3D said resist 30 is removed such that said thin film metallayer 23 remains on said first substrate 21.

In a last step the thin film metal layer 23 on the surface 22 of thefirst substrate 21 is brought into contact with a surface 25 of a secondsubstrate 24, such that a bonding between the second substrate 24 andthe thin film metal layer 23 on the first substrate 21 is provided, seeFIG. 3E. This bonding is then strengthened with use of a strengtheningstep as described above. A device 26 comprising two substrates 21, 24,an intermediate thin film metal layer 23 and two microstructures 20 isthus produced.

FIGS. 4A and 4B show two additional steps of the method of FIGS. 3A-3E,which two additional steps are to be performed optionally. FIG. 4A showsthe first substrate 21, the thin film metal layer 23 and the resist 30after etching the two microstructures 21, which figure corresponds toFIG. 3C. However, as FIG. 4A shows, parts 23A of the thin film metallayer 23 overlap the microstructures 20. This could for example be dueto an isotropic etching behaviour, in which an undercutting of the etchmask occurs. Due to that said parts 23A overlap, a surface 23B of theoverlapping parts 23A that is directed away from the resist 30 is notcovered by the resist 30 and the first substrate 21. This exposedsurface 23B of the overlapping part 23A is etched in order to adapt thewidth of the thin film metal layer 23 to the width of the microstructure20, see FIG. 4B. Said etching is performed by means of conventionaletching techniques and etching means, for example by means of wetchemical etching.

FIG. 5 shows a second embodiment of a device 36 produced by a fourthembodiment of the method according to the invention. In accordance withthe second embodiment of the method, in the second step, a thin filmmetal layer 33 is deposited on a cleaned surface 32 of a first substrate31 according to a predetermined pattern. The predetermined patterncomprises a first thin film metal layer 33A, which first layer 33Asurrounds a portion of the surface 32 of the first substrate 31, suchthat after the second substrate (not shown) is brought into contact withthe first substrate 31, said portion defines an inner space 38 betweensaid two substrates. The predetermined pattern further comprises asecond thin film metal layer 33B, which layer 33B extends from theinside of the inner space 38 to the outside of the inner space 38. Alaser is used for strengthening the bond over a laser weld 50A, 50B. Thelaser used has suitable power, for example higher than 100 mW, such thatthe thin film metal layers 33A, 33B of the welds 50A, 50B diffuse intoparts of the substrates that surround the welds 50A, 50B and thus thosewelds 50A, 50B become electrically non-conductive. These welds 50A, 50Bdefine unirradiated patterns in the layers 33A, 33B that remainelectrically conductive. The two unirradiated parts of the second layer33B separated by weld 50B form electrical connections between the insideof the inner space 38 and the outside of the inner space 38. By means ofweld 50A the inner space 38 is dust tight sealed. An electrical and/oroptical and/or a chemical component 37 is arranged within the innerspace 38. The device 36 may be cut over the dot line 60, which dot line60 is perpendicular with respect to the longitudinal direction of thesecond layer 33B, such that the part of the device 36 comprising theinner space 38 may be used as a separate device and the other part (onlypartly shown) may also be used as a separate device.

FIG. 5 further shows two irradiated patterns 150A, 150B, that crossthrough the metal layer 33A that surrounds the inner space 38. Bycrossing through the metal layer 33A said irradiated patterns 150A, 150Bbreak the electric circuit that would otherwise be formed by thesurrounding metal layer 33A. Said irradiated patterns 150A, 150B crossthe metal layer 33A in the transverse direction.

FIG. 6 shows a third embodiment of a device 46 produced by a fifthembodiment of the method according to the invention. In accordance withthe second and fourth embodiment of the method, in the second step, athin film metal layer 43 is deposited on a cleaned surface 42 of a firstsubstrate 41 according to a predetermined pattern. The predeterminedpattern comprises a thin film metal layer 43, which surrounds a portionof the surface 42 of the first substrate 41, such that after the secondsubstrate (not shown) is brought into contact with the first substrate41, said portion defines a part of an inner space 48 between said twosubstrates. A laser is used for strengthening the bond over a laser weld50A, 50B. As described above, as a result of the suitable laser power,the thin film metal layer 43 of the welds 50A, 50B diffuse into parts ofthe substrates that surround the welds 50A, 50B and thus those welds50A, 50B become electrically non-conductive. These welds 50A, 50B defineunirradiated patterns in the layer 43 that remain electricallyconductive and which patterns function as electrical connections betweenthe components 47. By means of weld 50A the inner space 48 ishermetically sealed. As described above, the device 46 may be cut overthe dot line 60, which dot line is perpendicular to the longitudinaldirection of the first substrate 41, such that the part of the device 46comprising the inner space 48 may be used as a separate device and theother part (only partly shown) may also be used as a separate device.

FIG. 7 shows a fourth embodiment of a device 56 produced by a sixthembodiment of the method according to the invention. In accordance withthe second and fourth embodiment of the method, in the second step, athin film metal layer 53 is deposited on a cleaned surface 52 of a firstsubstrate 51 according to a predetermined pattern. The predeterminedpattern comprises a thin film metal layer 53, which surrounds a portionof the surface 52 of the first substrate 51, such that after the secondsubstrate (not shown) is brought into contact with the first substrate51, said portion defines a part of an inner space 58 between said twosubstrates. A laser is used for strengthening the bond over a laser weld50, that extends in the longitudinal direction of the thin film metallayer 54 over the entire length thereof. As described above, as a resultof the suitable laser power, the thin film metal layer 53 of the weld 50diffuses into parts of the substrates that surround the weld 50 and thusbecomes weld 50 electrically non-conductive. By means of weld 50 theinner space 58 is hermetically sealed. Said laser is further used forforming a second laser weld or irradiated pattern 150 that extends inthe transverse direction of the thin film metal layer 54 over the entirewidth thereof. As a result of said irradiated pattern 150 crossingthrough the metal layer 53 that surrounds the inner space 58, saidirradiated pattern 150 breaks the electric circuit that would otherwisebe formed by the surrounding metal layer 53. As such, interference froma closed conduction circuit is prevented, such that the component 57located in the inner space may be any component sensitive tointerference from a closed conduction circuit, for example a magneticsensor or a wireless communication device.

It is noted that such an irradiated pattern crossing through the thinmetal layer is also shown in FIG. 5, as described above. FIG. 7 showsthat this feature according to the invention may also be applied withoutan electrical connection between the inside of the inner space to theoutside of the inner space.

The invention is not restricted to the variants shown in the drawing,but it also extends to other preferred embodiments that fall within thescope of the appended claims.

1. A method for bonding at least two substrates, for example made fromglass, silicon, ceramic, aluminum, or boron, characterized by using anintermediate thin film metal layer for providing the bonding, saidmethod comprising the following steps of: a) providing said twosubstrates; b) depositing said thin film metal layer on at least a partof a surface of a first substrate of the two substrates; c) bringing asurface of the second substrate into contact with said thin film metallayer on said surface of the first substrate such that a bonding betweenthe second substrate and the thin film metal layer on the firstsubstrate is provided; and d) at least locally strengthening the bondingbetween the second substrate and the thin film metal layer on the firstsubstrate.
 2. The method according to claim 1, wherein said thin filmmetal layer comprises a metal chosen from the group comprisingpalladium, copper, tungsten, aluminum, cobalt, nickel, thalium,ruthenium, iron, molybdenum, stainless steel, chromium, tantalum,vanadium and titanium, and wherein said thin film metal layer comprisesa metal oxide layer.
 3. The method according to claim 1, wherein saidthin film metal layer comprises a metal chosen from the group comprisingsilver, platinum and gold.
 4. The method according to claim 1, whereinstep d) is performed by urging the two substrates together.
 5. Themethod according to claim 1, wherein step (d) is performed by at leastlocally heating said thin film metal layer.
 6. The method according toclaim 5, wherein said heating is performed by means of a laser and atleast one of the substrates is transparent for said laser, an electriccurrent, microwave radiation or ultrasonic energy.
 7. The methodaccording to claim 1, wherein step (d) is performed by heating the twosubstrates and the intermediate thin film metal layer in an oven.
 8. Themethod according to claim 1, wherein step (d) is performed by applyingan underpressure, for example a vacuum, to the two substrates and theintermediate thin film metal layer.
 9. The method according to claim 1,wherein: at least one of the two substrates provided in step (a)comprises a cavity; step (b) is performed such that said thin film metallayer surrounds a portion of the surface of the first substrate; step(c) is performed such that after step (c), said portion, said cavity,and the inner surface of the thin film metal layer directed to saidportion, define an inner space between said two substrates, and step (d)is performed such that a sealing of the inner space between said twosubstrates is provided.
 10. The method according to claim 1, whereinstep (b) is performed such that it allows at least a part of said thinfilm metal layer to be used as an electrical connection and/or anoptical element and/or a chemical element.
 11. The method according toclaim 10, wherein step (b) is performed such that said part of said thinfilm metal layer that forms the electrical connection extends from theinside of the inner space to the outside of the inner space.
 12. Themethod according to claim 5, wherein said heating is performed byirradiating a predetermined pattern in the thin film metal layer bymeans of a laser, wherein at least one of the substrates is transparentfor said laser, wherein said pattern defines an unirradiated secondpattern that is electrically conductive.
 13. The method according toclaim 9, wherein said irradiated pattern crosses through saidsurrounding thin film metal layer in order to break an electricalcircuit of the thin film metal layer.
 14. The method according to claim12, wherein said unirradiated second pattern extends from the inside ofan inner space or the inner space to the outside of the inner space. 15.The method according to claim 1, wherein said thin film metal layer isbiocompatible.
 16. The method according to claim 1, comprising thesteps, to be performed after step (b) and before step (c), of: e)depositing a resist on said thin film metal layer; f) patterning saidresist and said thin film metal layer on said part of the surface of thefirst substrate; g) etching said first substrate comprising said thinfilm metal layer and said resist such that at least one microstructureis formed in said first substrate; and h) removing said resist such thatsaid thin film metal layer remains on said first substrate.
 17. Themethod according to claim 16, comprising the step, to be performed afterstep (g) and before step (h), of; i) etching parts of said thin filmmetal layer that overlap said microstructure to compensate forunderetching.
 18. The method according to claim 9, wherein the sealingof the inner space between said two substrates is hermetic, andcomprising the step of: j) arranging temperature-sensitive components inthe inner space.
 19. A device comprising two substrates and anintermediate thin film metal layer, which device comprises an innerspace between the two substrates, which inner space is surrounded bysaid intermediate thin film metal layer that hermetically seals theinner space, wherein the thin film metal layer is biocompatible, andwherein temperature-sensitive components are arranged in said innerspace.
 20. The device according to claim 19, wherein the two substratesindependently comprise a material selected from the group consisting ofglass, silicon, ceramic, aluminum and boron, and combinations thereof.